Detection of a common odd aberration in confocal reflection microscopy by means of an edge scan

In reflection laser scanning microscopes, detection of odd aberrations is challenging because aberration cancellation can occur after the second passage of the light beam through the system. A method is proposed that uses a sample containing high spatial frequencies, such as an edge scan, to detect and measure the presence of odd aberrations. The new approach is demonstrated by scanning the focal spot over an edge in a confocal reflection microscope when coma is present in the imaging system (a common odd aberration). It is shown that the edge response displays characteristic distortions which are typical of coma. Detection of amplitude, sign and orientation of the coma aberration is made possible by comparison of the measured edge responses with theoretical curves. (paper)